Elucidation of the Molecular Mechanisms of Action of the Natural Antimicrobial Peptide Subtilosin Against the Bacterial Vaginosis-associated Pathogen Gardnerella vaginalis

Subtilosin A is a 35-amino acid long cyclical peptide produced by Bacillus amyloliquefaciens that has potent antimicrobial activity against a variety of human pathogens, including the bacterial vaginosis-related Gardnerella vaginalis. The specific mode of action of subtilosin against G. vaginalis was elucidated by studying its effects on the proton motive force's (PMF) components: transmembrane electric potential (Delta Psi), transmembrane pH gradient (Delta pH), and intracellular ATP levels. The addition of subtilosin to G. vaginalis cells caused an immediate and total depletion of the Delta pH, but had no effect on the Delta Psi. Subtilosin also triggered an instant but partial efflux of intracellular ATP that was twofold higher than that of the positive control bacteriocin, nisin. Taken together, these data suggest that subtilosin inhibits G. vaginalis growth by creating transient pores in the cells' cytoplasmic membrane, leading to an efflux of intracellular ions and ATP and eventually cell death.